Renix XJ sputtering, Low Fuel Pressure

So for about the past two weeks when I really push the throttle, my Jeep sputters like it's running out of gas.

I put a new fuel pressure regulator on about three months ago. I checked the pressure on the rail, It's about 20psi with the vacuum on about 27 when off. I installed a new fuel pump and filter, and still read the same pressure. I'm gonna check the lines for some sort of obstruction tomorrow, what else could it be? I can't think of anything else that is in the fuel system. At cruising RPM there is no issue, only when I accelerate up hill or drive over 70 on the highway.

1990 Limited, Renix 4.0

Replace the regulator yet?

Check the hose between the pump and pick up tube.

I replaced a pump and cut that hose a little long. Turns out the hose clamp could not work that well with the extra hose pushed up the steel tube.

Fuel filter?

My Renix would run lean and crap out at around 2400 RPM when it was warm (at operating temperature) and again above 3500 RPM. It would run fine when it was cold, turned out to be the O2 sensor. Actually happened twice, once was the O2 sensor and the second time the O2 sensor harness was cooking on the exhaust manifold.

I also had mine run out of fuel at around 65 MPH, turned out to be the ballast resistor that time. Too little voltage making it to the pump. When I removed the ballast resistor the back side was completely disintegrated and scorched.

Also check your MAP vacuum line, the plastic vacuum line can rub through against a harness or whatever on the bottom and have a tiny pin hole in it. Which can cause fuel (air-fuel ratio) issues. Seen this on numerous Renix.

Thanks all, still haven't gotten anywhere other then to find out that the fuel pressure gauge isn't working right, so this might not even be a fuel issue. I checked the resistor. It appears to be working fine, also the map sensor. I'll check the O2. It's only a few years old, but I'm really scratching my head.

Re: Renix XJ sputtering, Not Low Fuel Pressure

So I found out that the gauge I was using to test pressure was bad. After a while it started reading zero psi. Got a new one am now getting 30 psi at idle and 37 with the vacuum disconnected. So I assume it isn't the fuel system, what else can it be? Maybe the computer is bad? I've disconnected and tested almost every sensor I can think of, but it still accelerates like crap.

Did you do a sweep test on the TPS?

Hypoid said:

Check the hose between the pump and pick up tube.

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x2

Re: Renix XJ sputtering, Not Low Fuel Pressure

Hypoid said:

Did you do a sweep test on the TPS?

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That's a good call, I did this about a year ago, but who knows it may have drifted or died.

As far as the hose between the pump and pickup tube, you mean the little hose on the pump assembly? I replaced the entire assembly already, and I appear to be in the right pressure zone around 30 PSI, the whole issue I was having with thinking this was low pressure was from a faulty test gauge borrowed from Oriley. :smsoap:

So I started looking towards the fuel injectors, For about the past 4 months since it cooled down for "winter" I have been having rough idling when the engine was cold. I discovered tonight that my first fuel injector isn't always working, while I don't think this is the culprit, replacing the injectors is definitely going to now be job #1.

Originally I thought the whole issue was an air intake issue and not a fuel issue, but the low pressure readings from the first faulty test gauge sent me down that rabbit hole. Now I'm starting to think maybe this is an exhaust issue. I believe the cat was changed out in 2012 before I purchased the vehicle, but it's possible it could have failed.

Nacho-1990 said:

I did this about a year ago, but who knows it may have drifted or died.

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You are looking for a dead spot as much as anything else.

Nacho-1990 said:

So I started looking towards the fuel injectors, For about the past 4 months since it cooled down for "winter" I have been having rough idling when the engine was cold. I discovered tonight that my first fuel injector isn't always working

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Good job on chasing down and verifying the fuel pressure. Try some fuel injector cleaner in the tank, old_man is a fan of this stuff: https://www.bgprod.com/catalog/gasoline-fuel-system/bg-44k-fuel-system-cleaner/

I didn't feel like typing about checking for a plugged CAT:

Not to pull out the plugs on weird stuff, but it could be ignition related as well. A weak coil will have the voltage to fire at low RPM, but not always at high RPMs.

Anecdotally, I had a bad spark plug which caused me to replace many parts before checking plugs (hey, they were new!) and it turned out there was no electrode. Guess I didn't gap that plug...or it disintegrated and blew out the exhaust or something. It would always sputter and act like it was out of gas when heavily loaded, going up long hills, etc. One $1.29 NGK later, and it ran like a dream. (They were Champions if anyone was curious.)

So I finally tracked it down. :sunshine:

After replacing the fuel injectors I still wasn't getting #1 to fire. I had replaced the spark plugs about two months ago but after confirming the impedance of the spark plug cable I discovered a minor crack in the ceramic of the spark plug. So the reason I was losing the power was not just the cylinder being dead, but it filling with fuel and bogging down the engine. :banghead:

Don't worry I already changed out the oil, there was a significant odor of gas in it.

Awesome! Doesn't it just kill ya when it's something that cheap and easy to replace??